1. Field of the Invention
The invention relates to transmissions that use power-take off units (“PTOs”). In particular, the invention relates to transmissions that interface with a PTO using a PTO drive gear.
2. Related Art
PTOs provide a convenient means to power accessories or secondary functions of a vehicle or other powered equipment. PTOs may be used with vehicles of all types, including, but not limited to, automobiles, trucks, marine vessels, or airplanes. A PTO may also be used with an industrial engine. A PTO may interface directly with an engine, or may interface with a transmission that is used with an engine. Generally, the output of a PTO is a shaft to which other devices or equipment can be attached and powered. For example, the output of a PTO may be used to power a hydraulic pump, winch, or dump truck bed lift. PTOs may be driven by any torque carrying shaft in the engine, transmission, or vehicle.
A common arrangement is an engine-driven PTO arrangement where the PTO receives an input torque from the engine crankshaft, or a component connected to the engine crankshaft. A common connection point for engine-driven PTO applications is the torque converter impeller, which may be directly connected to the engine crankshaft through a connection to the engine flex-plate.
Typically, in engine-driven PTO applications, excessive gear noises are generated at the interface between the drive gear, which may be a gear in a transmission, and the PTO input gear due to backlash. Backlash may be described as the amount of clearance or space between mating components such as gears. Components may generate noise due to their backlash, particularly when the components are unloaded. Noise typically occurs when the engine is operating at low revolutions per minute (“RPM”) due to torsional vibrations from the engine that excites the gear mesh of the drive gear and PTO input gear. Noise may also occur during PTO operation when the PTO is operating with a low torque load at the output side of PTO. This noise results in decreased efficiency and may be irritable or harmful to the operator of the vehicle or equipment that is driven by the PTO. Thus, there is a need for a PTO that offers reduced noise during operation, particularly when the PTO is operating with a low load or at low RPMs.